Cell C is a disappointment

I am very disappointed in Cell C my phone got switched off due to negligence I had 2 contracts with them the one expired so I told them lets end it and I will carry on with the current one the never cancelled it from their side and now demands the full payment because the never stopped the contract, now I am sitting with a contract phone that is still not working even though I still pay every month for the contract that is still active. Very bad service.